Method of alkylating polystyrene



United States Patent 3,388,111 METHOD OF ALKYLATING POLYSTYRENE RobertH. Allen and Larry D. Yats, Midland, Mich., as-

signors to The Dow Chemical Company, Midland, Mich, a corporation oiDelaware No Drawing. Continuation-impart of application Ser. No.350,126, Mar. 6, 1964. This application Feb. 9, 1967, Ser. No. 614,804

4 Claims. (Cl. 260-935) ABSTRACT OF THE DISCLOSURE A process foralkylating polystyrene which comprises contacting polystyrene dissolvedin an inert solvent with an alkyl ester of p-toluene sulfonic acid andBF at temperatures between 25 and 75 C.

This application is a continuation-in-part of our prior application Ser.No. 350,126 filed Mar. 6, 1964, now abandoned.

This invention relates to a method of alkylating polystyrene. Moreparticularly, it concerns the alkylation of polystyrene with an alkylsulfonate in the presence of a boron trifiuoride catalyst whereby thereis no significant amount of degradation of the polymer molecules.

Polystyrene has been used widely as a molding resin owing to its lowcost, ease of fabrication, light weight, etc. For some uses it isdesirable that the resin have high heat distortion, improved solventresistance and the like. These desirable properties can be provided, forexample, by grafting a reactive group on the aromatic nuclei of thepolymer so that they can be cross-linked with a reactive compound. Thus,this invention provides an improved method of attaching alkyl groups tothermoplastic polystyrene whereby reactive molecules can be attached tothe alkyl groups to reduce the plasticity of the resin or otherwisealter its physical properties.

Previous methods for alkylating polystyrene with an a-olefin in thepresence of a Friedel-Crafts catalyst have been handicapped by twoproblems. The highly active catalysts which are required to producealkylation break the polymer chains, thereby degrading the polymer intoa lower molecular weight resin. When low catalyst levels are used toavoid this problem of degradation, there is little alkylation of thepolystyrene and the long reaction time involved in attempting to producealkylation at the milder conditions results in homopolymerization of theolefin, particularly with the lower alkenes.

We have found that polystyrene can be alkylated with a low molecularweight alkane without degrading the polymer by reacting the polymer withan alkyl ester of p-toluene sulfonic acid in the presence of a BFcatalyst. In the presence of this catalyst the alkyl group is split fromthe ester and attached to an aromatic nucleus of the polymer, leavingthe sulfonic acid as a residue or by-product of the alkylation.

The method can be illustrated by the following examples describing thepropylation of polystyrene.

Example 1 26 parts by weight of polystyrene were dissolved in 494 partsof o-dichlorobenzene in a reaction chamber. 26.6 parts ofisopropyl-p-toluene sulfonate were added,

3,388,111 Patented June 11, 1968 ice then the solution stirred andheated to 50-55 C. BF was passed through the solution slowly for sixhours. At the end of that time the solution was washed with water torecover the polymer free of sulfonic acid, catalyst and solvent. Thepolystyrene used in this alkylation had a viscosity of 21.4 centipoisesin a 10 percent toluene solution at 25 C. The alkylated product had aviscosity of 23.2 centipoises at the same concentration and temperature,indicating there was no degradation of the polymer. Infra-red analysisshowed the product contained 0.4 isopropyl group per aromatic ring withmost of the isopropyl groups attached at the para position.

Example 2 This alkylation was conducted in the same manner as Example 1with the only difference being that the polystyrene had a highermolecular weight. The viscosity of a 10 percent solution in toluene at25 C. was 71 centipoises. The viscosity of the alkylated product was76.5 centipoises.

In addition to the isopropyl esters of p-toluene sulfonic acid, otheralkyl esters and particularly those of secondary alkyls such as those ofsecondary butyl and cyclohexyl may be used as the alkylating agent.

The solvent for the polystyrene and alkylating agent may be any ofnumerous solvents which are inert in the reaction mixture. In additionto the o-dichlorobenzene used in the examples above, we may usetrichlorobenzene, ethylene dichloride, carbon tetrachloride, methylenechloride, nitrobenzene and the like as solvents.

The alkylation can be carried out at temperatures between about 0 and100 C. and preferably 25 to 75 C. to get an economical reaction ratewithout significant polymer degradation. The reaction time is betweenabout 0.5 and 24 hours, depending on the temperature of the reactionmixture.

The amount of alkyl toluene sulfonate which may be used to alkylate thepolymer varies from about 0.01 to 3.0 moles of the sulfonate per mole ofaromatic nucleus in the polymer. At the lower mole ratio, i.e. 0.01, thepolymer would be very slightly alkylated so that little grafting orcross-linking could be produced. At the 3.0 mole ratio each aromaticring in the polymer would receive alkyl groups at three positions,producing a resin which has the potential of being highly grafted orcrosslinked. This highly alkylated polystyrene is difiicult to obtainowing to stearic hindrance.

The anhydrous BF catalyst is consumed in the alkylation so that it isnecessary to add it continuously during the reaction. This can beaccomplished quite easily by continuously bubbling the catalyst into thestirred reaction mixture. The pressure at which the alkylation isconducted is not critical. A pressure is ordinarily used which avoidsloss of solvent and provides sufiicient solubility of the gaseouscatalyst in the reaction mixture.

We claim:

1. In a method of alkylating polystyrene dissolved in an inert solventby reacting the polystyrene with an alkyl ester of p-toluene sulfonicacid, the improvement which consists in carrying out the reaction inadmixture with BF and a reaction temperature between 25 C. and 75 C.

2. A method according to claim 1 wherein the mole ratio of said alkylester to aromatic rings in said polystyrene is between about 0.01 and3:1.

3,388,111 3 4 3. A method of propylating polystyrene which c0mReferences Cited prises dissolving said polystyrene and isopropylp-toluene sulfonate in o-dichlorobenzene then passing BF through FOREIGNPATENTS said solution at temperatures between 25 and 75 C. 664,6921/1952 Great Britain.

4. A method of alkylating polystyrene which corn- 5 prises dissolvingpolystyrene and an alkyl ester of p-tol- OTHER REFERENCES uene sulfonicacid in an inert solvent and contacting said Chem. Abstracts, vol. 46,July-September 1952, p.

solution with BF at temperatures between 25 and 75 8043 0., whereby saidalkyl ester reacts with said polystyrene, then washing said solutionwith water, and separating 10 alkylpolymer free of solvent, catalyst,and p-toluene JAMES A SEIDLECK Primal}, Examiner sulfonic acid.

Chem. Abstracts, vol. 48, July-August 1954, p. 7558.

